001package org.cpsolver.studentsct.filter;
002
003import java.util.HashSet;
004
005import org.cpsolver.ifs.util.ToolBox;
006import org.cpsolver.studentsct.model.Student;
007
008
009/**
010 * This student filter accepts every student with the given probability. The
011 * choice for each student is remembered, i.e., if the student is passed to the
012 * filter multiple times the same answer is returned.
013 * 
014 * @version StudentSct 1.3 (Student Sectioning)<br>
015 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
016 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
017 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
018 * <br>
019 *          This library is free software; you can redistribute it and/or modify
020 *          it under the terms of the GNU Lesser General Public License as
021 *          published by the Free Software Foundation; either version 3 of the
022 *          License, or (at your option) any later version. <br>
023 * <br>
024 *          This library is distributed in the hope that it will be useful, but
025 *          WITHOUT ANY WARRANTY; without even the implied warranty of
026 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
027 *          Lesser General Public License for more details. <br>
028 * <br>
029 *          You should have received a copy of the GNU Lesser General Public
030 *          License along with this library; if not see
031 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
032 */
033public class RandomStudentFilter implements StudentFilter {
034    private double iProb = 1.0;
035    private HashSet<Long> iAcceptedStudentIds = new HashSet<Long>();
036    private HashSet<Long> iRejectedStudentIds = new HashSet<Long>();
037
038    /**
039     * Constructor
040     * 
041     * @param prob
042     *            probability of acceptance of a student
043     */
044    public RandomStudentFilter(double prob) {
045        iProb = prob;
046    }
047
048    /**
049     * A student is accepted with the given probability
050     */
051    @Override
052    public boolean accept(Student student) {
053        Long studentId = Long.valueOf(student.getId());
054        if (iAcceptedStudentIds.contains(studentId))
055            return true;
056        if (iRejectedStudentIds.contains(studentId))
057            return false;
058        boolean accept = (Math.random() < iProb);
059        if (accept)
060            iAcceptedStudentIds.add(studentId);
061        else
062            iRejectedStudentIds.add(studentId);
063        return accept;
064    }
065
066    /**
067     * Set acceptance probability. Update the sets of accepted and rejected
068     * students accordingly.
069     * 
070     * @param prob
071     *            new acceptance probability
072     */
073    public void setProbability(double prob) {
074        iProb = prob;
075        int accept = (int) Math.round(prob * (iAcceptedStudentIds.size() + iRejectedStudentIds.size()));
076        while (iAcceptedStudentIds.size() < accept && !iRejectedStudentIds.isEmpty()) {
077            Long studentId = ToolBox.random(iRejectedStudentIds);
078            iRejectedStudentIds.remove(studentId);
079            iAcceptedStudentIds.add(studentId);
080        }
081        while (iAcceptedStudentIds.size() > accept && !iAcceptedStudentIds.isEmpty()) {
082            Long studentId = ToolBox.random(iAcceptedStudentIds);
083            iRejectedStudentIds.add(studentId);
084            iAcceptedStudentIds.remove(studentId);
085        }
086    }
087
088    @Override
089    public String getName() {
090        return "Random";
091    }
092
093}